“…For each batch of activation experiments, specific proportions of the cathode material and spent graphite, and zirconia balls (3 mm diameter) were placed in the zirconia pot. The effects on the Li leaching efficiency of the cathode materials to spent graphite mass ratios (6,12,18,24,30,36,42, and 48 g g −1 ), ball-to-powder mass ratios (5,10,15,20, and 25 g g −1 ), mill rotation speeds (200, 400, 600, and 800 rpm), and rotation times (2, 4, 6, and 8 h) were investigated systematically. To prevent the equipment from overheating, the ball mill was operated continuously for 10 min with 10 min intervals.…”